LED constant current control circuit, control method and control chip

Abstract

The present application provides an LED constant current control circuit, a control method and a control chip, wherein the LED constant current control circuit includes: a threshold generation circuit, a threshold comparison circuit, a constant conduction detection circuit and a first switch; the constant conduction detection circuit is used to detect the working state of the first switch, and generate and output a threshold adjustment signal according to the working state; the threshold generation circuit is used to adjust the output first voltage threshold according to the threshold adjustment signal; the threshold comparison circuit is used to control the working state of the first switch according to the adjusted first voltage threshold. According to the LED constant current control circuit, by adjusting the first voltage threshold, the on and off timing of the first switch can be controlled to alleviate the problem of output current overshoot of the LED load.

Description

Technical Field

[0001] The present application relates to the technical field of electronic circuits, and in particular to an LED constant current control circuit, a control method and a control chip. Background Art

[0002] LED lamps are developing rapidly in the lighting industry due to their advantages such as low energy consumption, long life and low pollution. With the popularization of LED light sources, higher requirements are put forward for LED constant current drive control, requiring higher precision of LED constant current drive and lower LED drive cost. Hysteresis switch controllers are widely used in the prior art, which have the advantages of high constant current precision, low chip cost and large drive current. However, the control method of hysteresis switch also has inherent disadvantages, that is, when the input voltage is close to the rated voltage of LED, the hysteresis switch controller will be in a constant open state. Generally, the output current of LED at this time will be about 15% higher than the rated current. This is unacceptable for battery-powered applications, especially automotive lighting, and the output current of LED is 15% higher than the rated current, which will affect the life of LED. Summary of the invention

[0003] In view of this, the purpose of the present application is to provide an LED constant current control circuit, a control method and a control chip, which generate a threshold adjustment signal for controlling the first voltage threshold to drop or remain constant based on a switch control signal. By lowering the first voltage threshold, the timing of turning on and off the first switch can be controlled, so that the output current of the LED load is maintained within a specific voltage range. In this way, the problem of insufficient overshoot of the output current of the LED load when the input voltage is close to the rated voltage of the LED load can be alleviated.

[0004] The embodiment of the present application provides an LED constant current control circuit, the LED constant current control circuit comprising: a threshold generating circuit, a threshold comparing circuit, a constant conduction detection circuit and a first switch;

[0005] The constant-on detection circuit is used to detect the working state of the first switch (M1), and generate and output a threshold adjustment signal according to the working state;

[0006] The threshold generating circuit is used to adjust the output first voltage threshold according to the threshold adjustment signal;

[0007] The threshold comparison circuit is used to control the working state of the first switch according to the adjusted first voltage threshold.

[0008] Further, the threshold adjustment signal includes a first threshold adjustment signal and a second threshold adjustment signal;

[0009] The first threshold adjustment signal is a threshold adjustment signal for controlling the first voltage threshold to decrease;

[0010] The second threshold adjustment signal is a threshold adjustment signal for controlling the first voltage threshold to remain constant.

[0011] Further, when the constant-on detection circuit detects that the first switch is in the on state, it monitors the on time of the first switch and compares the on time of the first switch with a preset on time threshold;

[0012] When the on-time of the first switch is greater than the on-time threshold, a first threshold adjustment signal is generated and output;

[0013] When the on-time of the first switch is not greater than the on-time threshold, a second threshold adjustment signal is generated and output.

[0014] Further, the first input end of the threshold generating circuit is used to be connected to a first voltage source, the second input end of the threshold generating circuit is connected to the output end of the constant conduction detection circuit, and the input end of the constant conduction detection circuit is connected to the output end of the threshold comparison circuit;

[0015] The first input terminal of the threshold comparison circuit is used to input a sampling voltage, the second input terminal of the threshold comparison circuit is connected to the first output terminal of the threshold generation circuit to receive a first voltage threshold, the third input terminal of the threshold comparison circuit is connected to the second output terminal of the threshold generation circuit to receive a second voltage threshold, the output terminal of the threshold comparison circuit is connected to the first terminal of the first switch, and the threshold comparison circuit generates a switch control signal for controlling the first switch to be turned on or off based on the first voltage threshold and the second voltage threshold;

[0016] The second end of the first switch is used to be connected to one end of the power inductor, the other end of the power inductor is used to be connected to the LED load, and the third end of the first switch is grounded.

[0017] Further, the threshold generating circuit includes: an operational amplifier, a second switch, a first threshold generating circuit and a second threshold generating circuit;

[0018] The positive phase input terminal of the operational amplifier is used to be connected to the first voltage source, the negative phase input terminal of the operational amplifier is connected to the second detection point of the second threshold generating circuit, and the output terminal of the operational amplifier is connected to the first terminal of the second switch;

[0019] The second end of the second switch is used to be connected to a second voltage source, and the third end of the second switch is respectively connected to the first input end of the first threshold generating circuit and the input end of the second threshold generating circuit;

[0020] The output end of the first threshold generating circuit is connected to the second input end of the threshold comparison circuit, the second input end of the first threshold generating circuit is connected to the output end of the constant-on detection circuit, and the first threshold generating circuit is used to generate the first voltage threshold and adjust the output first voltage threshold according to the threshold adjustment signal;

[0021] The output terminal of the second threshold generating circuit is connected to the third input terminal of the threshold comparing circuit, and is used to generate a second voltage threshold and input it to the threshold comparing circuit, and the first voltage threshold is greater than the second voltage threshold.

[0022] Further, the first threshold generating circuit includes: a first resistor, a second resistor and a third resistor;

[0023] One end of the first resistor is connected to the third end of the second switch, the other end of the first resistor is connected to one end of the second resistor, the other end of the second resistor is connected to one end of the third resistor, and the other end of the third resistor is grounded;

[0024] A first detection point of the first threshold generating circuit is located between the first resistor and the second resistor, and the first detection point is connected to a second input terminal of the threshold comparing circuit.

[0025] Furthermore, the first threshold generating circuit further includes a third switch;

[0026] The first end of the third switch is connected to the output end of the constant-on detection circuit, the second end of the third switch is connected to one end of the third resistor, and the third end of the third switch is connected to the other end of the third resistor.

[0027] Further, the second threshold generating circuit includes: a fourth resistor, a fifth resistor, and a sixth resistor;

[0028] One end of the fourth resistor is connected to the third end of the second switch, the other end of the fourth resistor is connected to one end of the fifth resistor, the other end of the fifth resistor is connected to one end of the sixth resistor, and the other end of the sixth resistor is grounded;

[0029] The second detection point of the second threshold generating circuit is located between the fourth resistor and the fifth resistor, and the second detection point is connected to the negative phase input terminal of the operational amplifier;

[0030] The third detection point of the second threshold generating circuit is located between the fifth resistor and the sixth resistor, and the third detection point is connected to the third input terminal of the threshold comparing circuit.

[0031] Furthermore, the constant-on detection circuit includes: a CMOS circuit, a delay circuit and an inverter;

[0032] The input end of the CMOS circuit is connected to the output end of the threshold comparison circuit, the output end of the CMOS circuit is respectively connected to the first end of the delay circuit and the input end of the inverter, the power supply end of the CMOS circuit is used to be connected to a third voltage source, the ground end of the CMOS circuit is connected to the second end of the delay circuit, the third end of the delay circuit is grounded, and the output end of the inverter is connected to the second input end of the threshold generation circuit.

[0033] Further, the delay circuit includes: a first capacitor and a seventh resistor;

[0034] One end of the first capacitor is connected to the output end of the CMOS circuit, and the other end of the first capacitor is grounded. One end of the seventh resistor is connected to the ground end of the CMOS circuit, and the other end of the seventh resistor is grounded.

[0035] Furthermore, the LED constant current control circuit further includes: a current sampling circuit;

[0036] The current sampling circuit is used to detect the sampling current flowing through the LED load, and convert the sampling current into a corresponding sampling voltage, and output the sampling voltage to the threshold comparison circuit;

[0037] Furthermore, the first input terminal of the current sampling circuit is used to connect to a fourth voltage source, the second input terminal of the current sampling circuit is used to connect to an LED load, and the output terminal of the current sampling circuit is connected to the first input terminal of the threshold comparison circuit.

[0038] The embodiment of the present application further provides an LED constant current control method, which is applied to an LED constant current control circuit. The LED constant current control method includes:

[0039] The constant-on detection circuit detects the working state of the first switch, and generates and outputs a threshold adjustment signal according to the working state;

[0040] The threshold generating circuit adjusts the output first voltage threshold according to the threshold adjustment signal;

[0041] The threshold comparison circuit controls the working state of the first switch according to the adjusted first voltage threshold.

[0042] Further, the threshold adjustment signal includes a first threshold adjustment signal and a second threshold adjustment signal;

[0043] The first threshold adjustment signal is a threshold adjustment signal for controlling the first voltage threshold to decrease;

[0044] The second threshold adjustment signal is a threshold adjustment signal for controlling the first voltage threshold to remain constant.

[0045] The embodiment of the present application also provides an LED constant current control chip, including the LED constant current control circuit.

[0046] The LED constant current control circuit, control method and control chip provided in the embodiments of the present application can generate a threshold adjustment signal for controlling the first voltage threshold to decrease or remain constant based on a switch control signal, and control the timing of turning on and off of the first switch by lowering the first voltage threshold, so as to keep the output current of the LED load within a specific voltage range, so as to alleviate the problem of overshoot of the output current of the LED load when the input voltage is close to the rated voltage of the LED load.

[0047] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, preferred embodiments are specifically cited below and described in detail with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0049] Figure 1 A schematic diagram of the structure of a hysteresis switch controller in the prior art provided by an embodiment of the present application is shown;

[0050] Figure 2 The waveforms of various electrical quantities in the working process of the hysteresis switch controller in the prior art provided by the embodiment of the present application are shown;

[0051] Figure 3 A schematic diagram showing the relationship between the output current and the input voltage of the LED load of the hysteresis switch controller in the prior art provided by the embodiment of the present application is shown;

[0052] Figure 4 A structural block diagram of an LED constant current control circuit provided by an embodiment of the present application is shown;

[0053] Figure 5A schematic diagram of the structure of an LED constant current control circuit provided in an embodiment of the present application is shown;

[0054] Figure 6 A schematic diagram showing the relationship between the output current and the input voltage of the LED load provided in the embodiment of the present application is shown;

[0055] Figure 7 A schematic diagram showing the structure of a threshold value generating circuit provided in an embodiment of the present application is shown;

[0056] Figure 8 A schematic diagram of the structure of a constant-conduction detection circuit provided in an embodiment of the present application is shown;

[0057] Fig. 9 A schematic diagram showing the structure of a threshold comparison circuit provided in an embodiment of the present application is shown;

[0058] Fig.10 A structural schematic diagram of another LED constant current control circuit provided in an embodiment of the present application is shown;

[0059] Fig.11 A schematic diagram of the structure of a current sampling circuit provided in an embodiment of the present application is shown;

[0060] Fig.12 A flow chart of an LED constant current control method provided in an embodiment of the present application is shown. DETAILED DESCRIPTION

[0061] To make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. The components of the embodiments of the present application usually described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application claimed for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, each other embodiment obtained by those skilled in the art without making creative work belongs to the scope of protection of the present application.

[0062] It is found through research that hysteresis switch controllers are widely used in the prior art. Figure 1 Schematic diagram of the structure of the hysteresis switch controller in the prior art. Figure 1 ,like Figure 1The hysteresis switch controller shown is composed of a current sampling circuit, a threshold comparator and a power switch M0, where the power switch is NMOS. The advantages of the hysteresis switch controller are high constant current accuracy, low chip cost and large drive current. However, when the input voltage is close to the rated voltage of the LED load, the hysteresis switch controller will be in a constant on state, resulting in the output current of the LED load being about 15% higher than the rated current of the LED load, which is unacceptable for battery-powered applications, especially automotive lighting. In addition, the output current of the LED load is 15% higher than the rated current of the LED load, which will also affect the life of the LED.

[0063] Figure 2 FIG. 1 is a schematic diagram of the output current of a hysteresis switch controller in the prior art. Figure 2 As shown, the hysteresis switch controller uses two voltage thresholds VRH and VRL to limit the peak and valley values ​​of the sampling voltage respectively, wherein the sampling voltage can represent the voltage across the LED load, wherein VRH is the peak value of the sampling voltage, that is, when the sampling voltage rises to VRH, the PWM signal is a low-level signal to control the power switch M0 to turn off. At this time, the power inductor L releases energy, causing the sampling voltage to decrease, thereby causing the output current of the LED load to decrease; when the sampling voltage drops to VRL, the PWM signal is a high-level signal to control the power switch to close. At this time, due to the energy storage of the power inductor L, the sampling voltage increases, thereby increasing the output current of the LED load. Therefore, the average value of the sampling voltage can be set by the following formula VREF=(VRH+VRL) / 2. Furthermore, since the output current of the LED load is equal to the output current of the power inductor L, the average value of the output current of the LED load can be expressed as ILED=(VRH+VRL) / (2×RS)=VREF / RS, wherein VRH and VRL have the following relationship with VREF: VRH=1.15×VREF, and VRL=0.85×VREF.

[0064] Figure 3 FIG. 1 is a schematic diagram showing the relationship between the output current and input voltage of an LED load in the prior art. Figure 3As shown in the figure, when the input voltage VIN is much larger than the rated voltage VLED of the LED load, the output current ILED of the LED load remains constant. However, when the input voltage VIN is close to the rated voltage VLED of the LED load, that is, when the difference between the input voltage VIN and the rated voltage VLED of the LED load is less than a specific voltage value △V, the output current ILED of the LED load will increase by 1.15 times, where △V is approximately 1.15 times the sampling voltage VREF. The reason for the increase of the output current ILED of the above LED load by 1.15 times is that when the input voltage VIN is close to the rated voltage VLED of the LED load and the power switch M0 is closed, the output current ILED of the LED load can be expressed as: ILED=(VIN-VLED) / (RS+Rdson), where Rdson is the impedance when the power switch M0 is closed. If ILED×RS≤VRH at this time, the power switch M0 is turned on, and the output current ILED of the LED load is constant at (VIN-VLED) / (RS+Rdson). Because VRH=1.15×VREF, in critical cases, the output current ILED of the LED load can be expressed as: ILED=(VIN-VLED) / (RS+Rdson)=1.15×VREF / RS=1.15×ILED. It can be seen that when the input voltage VIN is close to the rated voltage VLED of the LED load, the output current ILED of the LED load will have a 15% overshoot, and the overshoot is proportional to VRH / VREF, that is, the larger the VRH, the greater the overshoot. This is the inherent architectural problem of the hysteresis switch controller.

[0065] In view of this, the present application provides an LED constant current control circuit to solve the problem in the prior art that when the input voltage is close to the rated voltage of the LED load, the output current of the LED load overshoots.

[0066] Figure 4 This is a structural block diagram of an LED constant current control circuit provided by an embodiment of the present application. Figure 4 As shown, the LED constant current control circuit includes: a threshold generating circuit 10, a threshold comparing circuit 20, a constant conduction detecting circuit 30 and a first switch M1.

[0067] Specifically, the constant-conduction detection circuit 30 is used to detect the working state of the first switch M1, and generate and output a threshold adjustment signal according to the working state; the threshold generation circuit 10 is used to adjust the output first voltage threshold according to the threshold adjustment signal; the threshold comparison circuit 20 is used to control the working state of the first switch M1 according to the adjusted first voltage threshold.

[0068] Here, the threshold adjustment signal includes a first threshold adjustment signal and a second threshold adjustment signal, wherein the first threshold adjustment signal is a threshold adjustment signal for controlling the first voltage threshold to decrease, and the second threshold adjustment signal is a threshold adjustment signal for controlling the first voltage threshold to remain constant.

[0069] Here, when the constant-on detection circuit 30 detects that the first switch M1 is in the on state, it monitors the on time of the first switch M1 and compares the on time of the first switch M1 with a preset on time threshold. When the on time of the first switch M1 is greater than the on time threshold, a first threshold adjustment signal is generated and output. When the on time of the first switch M1 is not greater than the on time threshold, a second threshold adjustment signal is generated and output.

[0070] As an example, the working state of the first switch M1 can be an on state and an off state. When the constant-on detection circuit 30 detects that the first switch M1 is in the on state, the on time of the first switch M1 is monitored. When the on time of the first switch M1 is greater than the on time threshold, a first threshold adjustment signal for controlling the first voltage threshold to drop is generated and output. When the on time of the first switch M1 is not greater than the on time threshold, a second threshold adjustment signal for controlling the first voltage threshold to remain constant is generated and output. The threshold comparison circuit 20 controls the on or off of the first switch M1 according to the adjusted first voltage threshold.

[0071] The following will be combined Figure 5 The structure and working principle of the LED constant current control circuit are explained in detail.

[0072] Figure 5 This is a schematic diagram of the structure of an LED constant current control circuit provided by an embodiment of the present application. Figure 5 As shown, the first input terminal of the threshold generating circuit 10 is used to be connected to the first voltage source V1. The second input terminal of the threshold generating circuit 10 is connected to the output terminal of the constant-on detection circuit 30. The input terminal of the constant-on detection circuit 30 is connected to the output terminal of the threshold comparison circuit 20. The first input terminal of the threshold comparison circuit 20 is used to input the sampling voltage. The second input terminal of the threshold comparison circuit 20 is connected to the first output terminal of the threshold generating circuit 10 to receive the first voltage threshold. The third input terminal of the threshold comparison circuit 20 is connected to the second output terminal of the threshold generating circuit 10 to receive the second voltage threshold. The output terminal of the threshold comparison circuit 20 is connected to the first terminal of the first switch M1. The threshold comparison circuit 20 generates a switch control signal for controlling the first switch M1 to be turned on or off based on the first voltage threshold and the second voltage threshold. The second terminal of the first switch M1 is used to be connected to one end of the power inductor L. The other end of the power inductor L is used to be connected to the LED load, and the third end of the first switch M1 is grounded.

[0073] The working principle of the LED constant current control circuit is as follows: the threshold generation circuit 10 generates a first voltage threshold and a second voltage threshold respectively based on the reference source voltage provided by the first voltage source V1. The first voltage threshold is greater than the second voltage threshold. The threshold comparison circuit 20 compares the sampled voltage with the first voltage threshold and the second voltage threshold, and generates a switch control signal for controlling the first switch M1 to turn on or off based on the comparison result. The sampled voltage can be detected by a conventional sampling circuit. The sampled voltage is used to characterize the voltage across the LED load.

[0074] When the first switch M1 is turned on, the power inductor L stores energy. Since the output current of the power inductor L is the same as the output current of the LED load, the output current of the LED load increases. When the first switch M1 is turned off, the power inductor L releases energy, and the output current of the LED load decreases. Among them, the first switch M1 can be a controllable switch tube such as MOSFET (Metal-Oxide-SemiconductorField-Effect Transistor) or IGBT (Insulated GateBipolar Transistor). At the same time, when the threshold comparison circuit 20 outputs a switch control signal for controlling the conduction of the first switch, the constant-on detection circuit 30 detects the duration of the switch control signal, and generates a threshold adjustment signal for controlling the reduction of the first voltage threshold or maintaining a constant according to the duration of the switch control signal. By reducing the first voltage threshold, the turn-on and turn-off timing of the first switch is controlled, so that the output current of the LED load is kept within a specific voltage range to alleviate the problem of overshoot of the output current of the LED load.

[0075] Based on the LED constant current control circuit provided in the embodiment of the present application, the following can be obtained: Figure 6 The relationship between the output current and input voltage of the LED load is shown in FIG. Figure 6 As shown, the horizontal axis is the input voltage of the LED constant current control circuit, the vertical axis is the output current of the LED load, VLED is the rated voltage of the LED load, and Iout is the rated current of the LED load. Figure 6 It can be seen that when the input voltage differs greatly from the rated voltage of the LED load, the output current of the LED load continues to rise steadily. When the input voltage is close to the rated voltage of the LED load, the output current of the LED load remains constant after increasing to the rated current of the LED load, and there is no current overshoot phenomenon.

[0076] The following will be combined Figure 7 The structure and working principle of the threshold generating circuit 10 are described in detail.

[0077] Figure 7 Schematic diagram of the structure of the threshold value generating circuit 10 provided in the embodiment of the present application. Figure 7 As shown, the threshold generating circuit 10 includes: an operational amplifier A1 , a second switch M2 , a first threshold generating circuit 101 and a second threshold generating circuit 102 .

[0078] Specifically, the positive input terminal of the operational amplifier A1 is used to connect to the first voltage source V1. The negative input terminal of the operational amplifier A1 is connected to the second detection point F2 of the second threshold generating circuit 102. The output terminal of the operational amplifier A1 is connected to the first terminal of the second switch M2. The second terminal of the second switch M2 is used to connect to the second voltage source V2. The third terminal of the second switch M2 is connected to the first input terminal of the first threshold generating circuit 101 and the input terminal of the second threshold generating circuit 102 respectively. The output terminal of the first threshold generating circuit 101 is connected to the second input terminal of the threshold comparison circuit 20. The second input terminal of the first threshold generating circuit 101 is connected to the output terminal of the constant-on detection circuit 30. The first threshold generating circuit 101 is used to generate a first voltage threshold and adjust the output first voltage threshold according to the threshold adjustment signal. The output terminal of the second threshold generating circuit 102 is connected to the third input terminal of the threshold comparison circuit 20. The second threshold generating circuit 102 is used to generate and output a second voltage threshold. Wherein, the first voltage threshold is greater than the second voltage threshold.

[0079] Based on the threshold value generating circuit 10 having the above structure, a first voltage threshold value and a second voltage threshold value can be generated and output respectively. Specifically, the first voltage source V1 generates a reference source voltage for the operational amplifier A1. The operational amplifier A1 adjusts the voltage of the second voltage source according to the reference source voltage and the voltage at the second detection point F2, so that the second voltage source V2 provides an operating voltage for the first threshold value generating circuit 101 and the second threshold value generating circuit 102, so that the first threshold value generating circuit 101 generates and outputs a first voltage threshold value, and the second threshold value generating circuit 102 generates and outputs a second voltage threshold value.

[0080] As an example, Figure 7 The second threshold generating circuit 102 shown includes: a fourth resistor R4, a fifth resistor R5 and a sixth resistor R6. One end of the fourth resistor R4 is connected to the third end of the second switch M2. The other end of the fourth resistor R4 is connected to one end of the fifth resistor R5. The other end of the fifth resistor R5 is connected to one end of the sixth resistor R6. The other end of the sixth resistor R6 is grounded. The second detection point F2 of the second threshold generating circuit 102 is located between the fourth resistor R4 and the fifth resistor R5. The second detection point F2 is connected to the negative phase input terminal of the operational amplifier A1. The third detection point of the second threshold generating circuit 102 is located between the fifth resistor R5 and the sixth resistor R6. The third detection point F3 is connected to the third input terminal of the threshold comparison circuit 20.

[0081] Based on the second threshold value generating circuit 102 having the above structure, when the second switch M2 is turned on, the fourth resistor R4, the fifth resistor R5 and the sixth resistor R6 in the second threshold value generating circuit 102 are connected in series in sequence. The voltage at the second detection point F2 is input into the operational amplifier A1 as the negative phase input terminal voltage of the operational amplifier A1. The voltage at the third detection point F3 is input into the threshold value comparison circuit 20 as the second voltage threshold. Then, the factors affecting the second voltage threshold are the sizes of the fourth resistor R4, the fifth resistor R5 and the sixth resistor R6.

[0082] As an example, Figure 7 The first threshold generating circuit 101 of the threshold generating circuit 10 shown includes: a first resistor R1, a second resistor R2 and a third resistor R3. One end of the first resistor R1 is connected to the third end of the second switch M2. The other end of the first resistor R1 is connected to one end of the second resistor R2. The other end of the second resistor R2 is connected to one end of the third resistor R3. The other end of the third resistor R3 is grounded. The first detection point F1 of the first threshold generating circuit 101 is located between the first resistor R1 and the second resistor R2. The first detection point F1 is connected to the second input end of the threshold comparison circuit 20.

[0083] Based on the first threshold value generating circuit 101 having the above structure, when the second switch M2 is turned on, the first resistor R1, the second resistor R2 and the third resistor R3 in the first threshold value generating circuit 101 are connected in series in sequence. The voltage at the first detection point F1 is input as the first voltage threshold to the threshold value comparison circuit 20. Then, the factors affecting the first voltage threshold are the sizes of the first resistor R1, the second resistor R2 and the third resistor R3.

[0084] As an example, Figure 7 The first threshold generating circuit 101 shown further includes a third switch M3. A first end of the third switch M3 is connected to the output end of the constant-on detection circuit 30. A second end of the third switch M3 is connected to one end of the third resistor R3. A third end of the third switch M3 is connected to the other end of the third resistor R3.

[0085] Based on the first threshold generating circuit 101 having the above structure, when the third switch M3 is turned on, the third switch M3 is equivalent to a wire, and the third resistor R3 is short-circuited, and the first resistor R1 and the second resistor R2 are connected in series in the first threshold generating circuit 101. The voltage at the first detection point F1 is still input into the threshold comparison circuit 20 as the first voltage threshold. Then, the factors affecting the first voltage threshold are the size of the first resistor R1 and the second resistor R2. When the third switch M3 is turned off, the structure of the first threshold generating circuit 101 is similar to that when the third switch M3 is not included, and the factors affecting the first voltage threshold are still the size of the first resistor R1, the second resistor R2 and the third resistor R3. Among them, the third switch M3 can be a controllable switch tube such as MOSFET or IGBT.

[0086] Then, without changing the resistance, when the third switch M3 is turned on, the third resistor R3 is short-circuited, causing the first voltage threshold to drop. When the third switch M3 is turned off, the first voltage threshold remains constant. It can be seen that based on the first threshold generating circuit 101 with the above structure, by controlling the conduction or disconnection of the third switch M3, the first voltage threshold can be controlled to decrease or remain constant.

[0087] Specifically, when the third switch M3 is turned on, the reference source voltage has a relationship with the first voltage threshold and the second voltage threshold as shown in the following equation:

[0088] , (1)

[0089] (1) In the formula, VRH is the first voltage threshold, VRL is the second voltage threshold, and VREF is the reference source voltage.

[0090] When the third switch M3 is turned off, the reference source voltage has a relationship with the first voltage threshold and the second voltage threshold as shown in the following equation:

[0091] , (2)

[0092] It can be seen from the above equations (1) and (2) that the first threshold generating circuit 101 can control the first voltage threshold to be reduced to the average value of the first voltage threshold and the second voltage threshold.

[0093] The threshold adjustment signal for controlling the third switch M3 in the threshold generation circuit 10 to turn on or off is generated by the constant-on detection circuit 30. Figure 8 The structure and working principle of the constant conduction detection circuit 30 are specifically described by taking an example.

[0094] Figure 8 Schematic diagram of the structure of the constant conduction detection circuit 30 provided in this embodiment. Figure 8As shown, the constant-on detection circuit 30 includes: a CMOS circuit 301 , a delay circuit 302 and an inverter 303 .

[0095] Specifically, the embodiment of the present application adopts a constant-on detection circuit 30 with a unilateral delay function. Among them, the input end of the CMOS circuit 301 is connected to the output end of the threshold comparison circuit 20. The output end of the CMOS circuit 301 is respectively connected to the first end of the delay circuit 302 and the input end of the inverter 303. The power supply end of the CMOS circuit 301 is used to connect to the third voltage source V3. The ground end of the CMOS circuit 301 is connected to the second end of the delay circuit 302. The third end of the delay circuit 302 is grounded. The output end of the inverter 303 is connected to the second input end of the threshold generation circuit 10.

[0096] As an example, the delay circuit 302 includes: a first capacitor C1 and a seventh resistor R7. One end of the first capacitor C1 is connected to the output end of the CMOS circuit 301. The other end of the first capacitor C1 is grounded. One end of the seventh resistor R7 is connected to the ground end of the CMOS circuit 301. The other end of the seventh resistor R7 is grounded.

[0097] Based on the constant conduction detection circuit 30 with the above structure, the working state of the first switch is determined by the switch control signal, and the threshold adjustment signal is generated according to the delay of the working state of the first switch. Among them, the switch control signal includes: a first control signal for controlling the conduction of the first switch M1, and a second control signal for controlling the turn-off of the first switch M1. The constant conduction detection circuit 30 will only generate and output the threshold adjustment signal for controlling the conduction or turn-off of the third switch M3 in the first threshold generation circuit 101 when the switch control signal is the first control signal for controlling the conduction of the first switch M1. Specifically, the method for generating the threshold adjustment signal is: when the switch control signal is the first control signal for controlling the conduction of the first switch M1, the conduction time of the first switch M1 is monitored. When the conduction time of the first switch M1 is greater than the pre-set conduction time threshold, the constant conduction detection circuit 30 generates and outputs the first threshold adjustment signal for controlling the decrease of the first voltage threshold. The first threshold adjustment signal is used to control the conduction of the third switch M3. When the on-time of the first switch M1 is not greater than the preset on-time threshold, the constant-on detection circuit 30 generates and outputs a second threshold adjustment signal for controlling the first voltage threshold to remain constant. The second threshold adjustment signal is used to control the third switch M3 to turn off.

[0098] As an example, the switch control signal for controlling the first switch M1 to be turned on can be a high-level signal. That is, when the switch control signal is a high-level signal, the first switch M1 is turned on, then the constant-conduction detection circuit 30 can generate a threshold adjustment signal according to the duration of the high-level signal. Specifically, when the duration of the high-level signal is greater than the preset on-time threshold, the constant-conduction detection circuit 30 generates and outputs a high-level signal to control the third switch M3 of the first threshold generating circuit 101 to be turned on. When the duration of the high-level signal is not greater than the preset on-time threshold, the constant-conduction detection circuit 30 generates and outputs a low-level signal to control the third switch M3 of the first threshold generating circuit 101 to be turned off. Among them, the duration threshold should be set within a time range of 20-50μs to accurately control the on and off timing of the third switch M3.

[0099] The switch control signal detected by the constant-on detection circuit 30 is generated by the threshold comparison circuit 20. Fig. 9 The structure and working principle of the threshold comparison circuit 20 will be described in detail.

[0100] Fig. 9 Schematic diagram of the structure of the threshold comparison circuit 20 provided in this embodiment. Fig. 9 As shown, the threshold comparison circuit 20 includes: a first comparator COMP1, a second comparator COMP2, a first NAND logic gate U1, a second NAND logic gate U2 and a first NOT logic gate U3.

[0101] Specifically, the positive phase input terminal of the first comparator COMP1 is connected to the first detection point F1 of the first threshold generating circuit 101 to input the first voltage threshold. The negative phase input terminal of the first comparator COMP1 is used to input the sampling voltage. The output terminal of the first comparator COMP1 is connected to the first input terminal of the first NAND logic gate U1. The positive phase input terminal of the second comparator COMP2 is used to input the sampling voltage. The negative phase input terminal of the second comparator COMP2 is connected to the third detection point F3 of the second threshold generating circuit to input the second voltage threshold. The output terminal of the second comparator COMP2 is connected to the first input terminal of the second NAND logic gate U2. The second input terminal of the first NAND logic gate U1 is connected to the output terminal of the second NAND logic gate U2. The output terminal of the first NAND logic gate U1 is connected to the first NAND logic gate U3. The second input terminal of the second NAND logic gate U2 is connected to the output terminal of the first NAND logic gate U1. The output terminal of the first NAND logic gate U3 is connected to the first switch M1 to output a switch control signal for controlling the first switch M1 to be turned on or off.

[0102] Based on the threshold comparison circuit 20 having the above structure, the sampled voltage can be compared with the first voltage threshold and the second voltage threshold, and a switch control signal for controlling the first switch M1 to be turned on or off is generated and output according to the comparison result. The switch control signal includes: a first control signal for controlling the first switch M1 to be turned on, and a second control signal for controlling the first switch M1 to be turned off. Specifically, when the sampled voltage is less than the second voltage threshold, the threshold comparison circuit 20 generates and outputs the first control signal for controlling the first switch M1 to be turned on. When the sampled voltage is greater than the first voltage threshold, the threshold comparison circuit 20 generates and outputs the second control signal for controlling the first switch M1 to be turned off.

[0103] As an example, the first control signal for controlling the first switch M1 to be turned on may be a high-level signal. The second signal for controlling the first switch M1 to be turned off may be a low-level signal. That is, when the sampled voltage is greater than the first voltage threshold, the threshold comparison circuit 20 outputs a low-level signal to control the first switch M1 to be turned off. At this time, the power inductor L releases energy, thereby reducing the output current of the LED load, and the sampled voltage also decreases accordingly. When the sampled voltage decreases to the second voltage threshold, the threshold comparison circuit 20 outputs a high-level signal to control the first switch M1 to be turned on. At this time, the power inductor L stores energy, thereby increasing the output current of the LED load.

[0104] Furthermore, after the first voltage threshold is adjusted, the first voltage threshold can be reduced to an average value of the first voltage threshold and the second voltage threshold. Then, the relationship between the output current of the LED load and the first voltage threshold and the second voltage threshold can be expressed by the following formula:

[0105] , (3)

[0106] In the formula (3), ILED is the output current of the LED load, RS is the sampling resistor (ie, the eighth resistor R8 in the embodiment of the present application), and Rdson is the on-resistance of the first switch M1.

[0107] The relationship between the output current at both ends of the LED load and the first voltage threshold and the second voltage threshold that can be achieved by the switch controller in the prior art is:

[0108] , (4)

[0109] It can be seen that the LED constant current control current provided by the present application can ensure that the output current of the LED load does not overshoot.

[0110] The sampling voltage input to the threshold comparison circuit 20 is generated by the current sampling circuit 40 .

[0111] The current sampling circuit 40 is used to detect the sampling current flowing through the LED load, and convert the sampling current into a corresponding sampling voltage, and output the sampling voltage to the threshold comparison circuit 20. The current sampling circuit 40 can be connected to the LED load to detect the sampling current flowing through the LED load, or connected to the power inductor L to detect the sampling current flowing through the LED load, or connected to other loads on the LED working circuit to detect the sampling current flowing through the LED load, and the applicant does not make any limitation here.

[0112] See also Fig.10 , Fig.10 This is a schematic diagram of another LED constant current control circuit provided by the embodiment of the present application. Fig.10 As shown, the first input terminal of the current sampling circuit 40 is used to connect to the fourth voltage source V4, the second input terminal of the current sampling circuit 40 is used to connect to the LED load, and the output terminal of the current sampling circuit 40 is connected to the first input terminal of the threshold comparison circuit 20.

[0113] The following will be combined Fig.11 The structure and working principle of the current sampling circuit 40 are described in detail.

[0114] Fig.11 Schematic diagram of the structure of the current sampling circuit 40 provided in this embodiment. Fig.11 As shown, the current sampling circuit 40 includes: an eighth resistor R8, a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, a fourth switch Q1, a fifth switch Q2, a sixth switch Q3, a first current load I1 and a second current load I2.

[0115] Specifically, one end of the eighth resistor R8 is connected to one end of the fourth voltage source V4 and the tenth resistor R10, respectively. The other end of the eighth resistor R8 is connected to one end of the ninth resistor R9. The other end of the ninth resistor R9 is connected to the first end of the fourth switch Q1. The second end of the fourth switch Q1 is connected to one end of the first current load I1 and the third end of the sixth switch Q3, respectively. The other end of the first current load I1 is grounded. The other end of the tenth resistor R10 is connected to the first end of the fifth switch Q2 and the first end of the sixth switch Q3, respectively. The second end of the fifth switch Q2 is connected to one end of the second current load I2. The other end of the second current load I2 is grounded. The second end of the sixth switch Q3 is connected to one end of the eleventh resistor R11. The other end of the eleventh resistor R11 is grounded. In addition, a fourth detection point F4 is set between the eighth resistor R8 and the ninth resistor R9. The fourth detection point F4 is connected to the LED load. The sampled current of the detected LED load is input to the current sampling circuit 40 through the fourth detection point F4. A fifth detection point F5 is set between the sixth switch Q3 and the eleventh resistor R11. The fifth detection point F5 is connected to the first input terminal of the threshold comparison circuit 20 , and is used to input the generated sampling voltage to the threshold comparison circuit 20 .

[0116] Based on the current sampling circuit 40 with the above structure, the fourth voltage source V4 is used to provide input voltage for the entire LED constant current control circuit, so that the sampling current flowing through the LED load can be detected and converted into a corresponding sampling voltage, which is output to the threshold comparison circuit 20.

[0117] Based on the LED constant current control circuit with the above structure, when the input voltage differs greatly from the rated voltage of the LED load, the LED constant current control circuit is equivalent to the existing hysteresis switch controller. When the input voltage is close to the rated voltage of the LED load, the constant-on detection circuit 30 in the LED constant current control circuit will continue to output a high-level signal to control the first voltage threshold to be reduced to the average value of the first voltage threshold and the second voltage threshold. Further, the threshold comparison circuit 20 is made to continuously output a low-level signal to control the first switch to be turned off, so that the output current of the LED load is stabilized within a reasonable range to prevent the output current of the LED load from overshooting, and at the same time, the LED constant current control circuit is always in a working state.

[0118] The LED constant current control circuit provided in the embodiment of the present application can generate a threshold adjustment signal for controlling the first voltage threshold to decrease or remain constant based on the switch control signal. By lowering the first voltage threshold, the timing of turning on and off the first switch can be controlled, so that the output current of the LED load is kept within a specific voltage range. In this way, the problem of insufficient overshoot of the output current of the LED load when the input voltage is close to the rated voltage of the LED load can be alleviated.

[0119] Based on the same inventive concept, an LED constant current control method corresponding to the LED constant current control circuit is also provided in the embodiment of the present application. Since the principle of solving the problem by the device in the embodiment of the present application is similar to the above-mentioned method in the embodiment of the present application, the implementation of the device can refer to the implementation of the method, and the repeated parts will not be repeated.

[0120] See also Fig.12 , Fig.12 This is a flow chart of a LED constant current control method provided by an embodiment of the present application. Fig.12 As shown, the LED constant current control method includes:

[0121] S1201. The constant-on detection circuit detects a working state of the first switch, and generates and outputs a threshold adjustment signal according to the working state.

[0122] S1202: The threshold generating circuit adjusts a first voltage threshold output according to the threshold adjustment signal.

[0123] S1203: The threshold comparison circuit controls the working state of the first switch according to the adjusted first voltage threshold.

[0124] Further, the threshold adjustment signal includes a first threshold adjustment signal and a second threshold adjustment signal;

[0125] The first threshold adjustment signal is a threshold adjustment signal for controlling the first voltage threshold to decrease;

[0126] The second threshold adjustment signal is a threshold adjustment signal for controlling the first voltage threshold to remain constant.

[0127] Specifically, the implementation process of the LED constant current control method is as follows: the constant conduction detection circuit generates a threshold adjustment signal by detecting the working state of the first switch. When the first switch is in the on state, the on time of the first switch is monitored. When the on time is greater than the preset duration threshold, a first threshold adjustment signal for controlling the first voltage threshold to drop is generated. The threshold generation circuit adjusts the size of the first voltage threshold accordingly, and inputs the adjusted first voltage threshold to the threshold comparison circuit. The threshold comparison circuit controls the on or off of the first switch according to the adjusted first voltage threshold. When the first switch is on, the output current of the LED load increases. When the first switch is off, the output current of the LED load decreases. By lowering the first voltage threshold to control the on and off timing of the first switch, the output current of the LED load is kept within a specific voltage range to alleviate the problem of output current overshoot of the LED load.

[0128] The LED constant current control method provided in the embodiment of the present application can generate a threshold adjustment signal for controlling the first voltage threshold to decrease or remain constant based on the switch control signal. By lowering the first voltage threshold, the timing of turning on and off the first switch can be controlled, so that the output current of the LED load is kept within a specific voltage range. In this way, the problem of insufficient overshoot of the output current of the LED load when the input voltage is close to the rated voltage of the LED load can be alleviated.

[0129] Finally, it should be noted that the above-described embodiments are only specific implementation methods of the present application, which are used to illustrate the technical solutions of the present application, rather than to limit them. The protection scope of the present application is not limited thereto. Although the present application is described in detail with reference to the above-mentioned embodiments, ordinary technicians in the field should understand that any technician familiar with the technical field can still modify the technical solutions recorded in the above-mentioned embodiments within the technical scope disclosed in the present application, or can easily think of changes, or make equivalent replacements for some of the technical features therein; and these modifications, changes or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. An LED constant current control circuit, characterized in that: The LED constant current control circuit comprises: a threshold generating circuit (10), a threshold comparing circuit (20), a constant current detecting circuit (30) and a first switch (M1); The constant-on detection circuit (30) is used to detect the working state of the first switch (M1), and to generate and output a threshold adjustment signal according to the working state; The threshold generating circuit (10) is used for adjusting the output first voltage threshold according to the threshold adjustment signal; The threshold comparison circuit (20) is used to control the working state of the first switch (M1) according to the adjusted first voltage threshold; The threshold adjustment signal includes a first threshold adjustment signal and a second threshold adjustment signal; The first threshold adjustment signal is a threshold adjustment signal for controlling the first voltage threshold to decrease; The second threshold adjustment signal is a threshold adjustment signal for controlling the first voltage threshold to remain constant; When the constant-on detection circuit (30) detects that the first switch (M1) is in the on state, it monitors the on time of the first switch (M1) and compares the on time of the first switch (M1) with a preset on time threshold; When the on-time of the first switch (M1) is greater than the on-time threshold, a first threshold adjustment signal is generated and output; When the on-time of the first switch (M1) is not greater than the on-time threshold, a second threshold adjustment signal is generated and output.

2. The LED constant current control circuit according to claim 1, characterized in that: The first input end of the threshold generating circuit (10) is used to be connected to a first voltage source (V1), the second input end of the threshold generating circuit (10) is connected to the output end of the constant-on detection circuit (30), and the input end of the constant-on detection circuit (30) is connected to the output end of the threshold comparison circuit (20); The first input terminal of the threshold comparison circuit (20) is used to input a sampling voltage, the second input terminal of the threshold comparison circuit (20) is connected to the first output terminal of the threshold generation circuit (10) to receive a first voltage threshold, the third input terminal of the threshold comparison circuit (20) is connected to the second output terminal of the threshold generation circuit (10) to receive a second voltage threshold, the output terminal of the threshold comparison circuit (20) is connected to the first terminal of the first switch (M1), and the threshold comparison circuit (20) generates a switch control signal for controlling the first switch (M1) to be turned on or off based on the first voltage threshold and the second voltage threshold; The second end of the first switch (M1) is used to be connected to one end of the power inductor (L), the other end of the power inductor (L) is used to be connected to the LED load, and the third end of the first switch (M1) is grounded.

3. The LED constant current control circuit according to claim 2, characterized in that: The threshold value generating circuit (10) comprises: an operational amplifier (A1), a second switch (M2), a first threshold value generating circuit (101) and a second threshold value generating circuit (102); The positive phase input terminal of the operational amplifier (A1) is used to be connected to the first voltage source (V1), the negative phase input terminal of the operational amplifier (A1) is connected to the second detection point F2 of the second threshold generating circuit (102), and the output terminal of the operational amplifier (A1) is connected to the first terminal of the second switch (M2); The second end of the second switch (M2) is used to be connected to a second voltage source (V2), and the third end of the second switch (M2) is respectively connected to a first input end of the first threshold generating circuit (101) and an input end of the second threshold generating circuit (102); The output end of the first threshold generating circuit (101) is connected to the second input end of the threshold comparison circuit (20), the second input end of the first threshold generating circuit (101) is connected to the output end of the constant-on detection circuit (30), and the first threshold generating circuit (101) is used to generate the first voltage threshold and adjust the output first voltage threshold according to the threshold adjustment signal; The output end of the second threshold generating circuit (102) is connected to the third input end of the threshold comparison circuit (20) for generating a second voltage threshold and inputting the second voltage threshold into the threshold comparison circuit (20), wherein the first voltage threshold is greater than the second voltage threshold.

4. The LED constant current control circuit according to claim 3, characterized in that: The first threshold generating circuit (101) comprises: a first resistor (R1), a second resistor (R2) and a third resistor (R3); One end of the first resistor (R1) is connected to the third end of the second switch (M2), the other end of the first resistor (R1) is connected to one end of the second resistor (R2), the other end of the second resistor (R2) is connected to one end of the third resistor (R3), and the other end of the third resistor (R3) is grounded; The first detection point F1 of the first threshold generating circuit (101) is located between the first resistor (R1) and the second resistor (R2), and the first detection point F1 is connected to the second input terminal of the threshold comparison circuit (20); The first threshold generating circuit (101) further includes a third switch (M3); The first end of the third switch (M3) is connected to the output end of the constant-on detection circuit (30), the second end of the third switch (M3) is connected to one end of the third resistor (R3), and the third end of the third switch (M3) is connected to the other end of the third resistor (R3).

5. The LED constant current control circuit according to claim 3, characterized in that: The second threshold generating circuit (102) comprises: a fourth resistor (R4), a fifth resistor (R5), and a sixth resistor (R6); One end of the fourth resistor (R4) is connected to the third end of the second switch (M2), the other end of the fourth resistor (R4) is connected to one end of the fifth resistor (R5), the other end of the fifth resistor (R5) is connected to one end of the sixth resistor (R6), and the other end of the sixth resistor (R6) is grounded; The second detection point F2 of the second threshold generating circuit (102) is located between the fourth resistor (R4) and the fifth resistor (R5), and the second detection point F2 is connected to the negative phase input terminal of the operational amplifier (A1); The third detection point F3 of the second threshold generating circuit (102) is located between the fifth resistor (R5) and the sixth resistor (R6), and the third detection point F3 is connected to the third input terminal of the threshold comparing circuit (20).

6. The LED constant current control circuit according to claim 1, characterized in that: The LED constant current control circuit further comprises: a current sampling circuit (40); The current sampling circuit (40) is used to detect a sampling current flowing through the LED load, convert the sampling current into a corresponding sampling voltage, and output the sampling voltage to the threshold comparison circuit (20).

7. A method for controlling a constant current of an LED, characterized in that: The LED constant current control method is applied to the LED constant current control circuit according to any one of claims 1 to 6, and the LED constant current control method comprises: The constant-on detection circuit (30) detects the working state of the first switch, and generates and outputs a threshold adjustment signal according to the working state; The threshold generating circuit (10) adjusts the output first voltage threshold according to the threshold adjustment signal; The threshold comparison circuit (20) controls the working state of the first switch according to the adjusted first voltage threshold; The threshold adjustment signal includes a first threshold adjustment signal and a second threshold adjustment signal; The first threshold adjustment signal is a threshold adjustment signal for controlling the first voltage threshold to decrease; The second threshold adjustment signal is a threshold adjustment signal for controlling the first voltage threshold to remain constant; When the constant-on detection circuit (30) detects that the first switch (M1) is in the on state, it monitors the on time of the first switch (M1) and compares the on time of the first switch (M1) with a preset on time threshold; When the on-time of the first switch (M1) is greater than the on-time threshold, a first threshold adjustment signal is generated and output; When the on-time of the first switch (M1) is not greater than the on-time threshold, a second threshold adjustment signal is generated and output.

8. An LED constant current control chip, characterized in that: It comprises the LED constant current control circuit as described in any one of claims 1 to 6.

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